1. Field of the Invention
The present invention relates to a printer-incorporated electronic still camera and a printing method for an optical printer wherein a fluorescent display tube or panel is driven as a light source of a printing head based on electronic image data.
2. Background Arts
Portable electronic still cameras are widely known, that obtain electronic images from optical images of subjects through an imaging device, such as a CCD image sensor, and stores the electronic images in a memory in the form of digital image data. Also an electronic still camera having a printer incorporated therein has been known. An example of this type of electronic still camera is disclosed in JPA 11-127409, wherein a self-developing type photo film sheet, called an instant film, is used as a recording medium for printing an image thereon, so an optical printer is driven based on the image data read out from the memory, to photograph or optically record an image on the instant film.
The optical printer uses a recording head that is elongated in a main scan direction across an exposure surface of the instant film, and projects three color light beams onto the exposure surface while moving in parallel to the exposure surface in a sub scan direction perpendicular to the main scan direction. In this way, the image is recorded line after line on the instant film. The recording head is constituted of a liquid crystal array of a large number of light-permeable type liquid crystal segments which are driven each individually in accordance with print data of each pixel, an elongated fluorescent lamp for illuminating the liquid crystal array, and an optical system for directing exposure light beams from the liquid crystal array to the exposure surface of the instant film.
Recently, a study has been made to minimize the recording head by replacing the fluorescent lamp and the liquid crystal array with a fluorescent display panel. The fluorescent display panel is constituted of a micro light emitting elements arranged in a raw, and each light emitting element corresponds to one pixel, so the light intensity of each light emitting element may be controlled individually in accordance with the print data of the corresponding pixel.
FIG. 11 shows an example of fluorescent display panel 100. The fluorescent display tube 100 has a front glass 101 and a glass substrate 102 that constitute a vacuum container, in which a filament 103 as a cathode, a grid 104 and an anode 105 are contained as fundamental electrodes. Many kinds of metal parts and a coating layer 106 are also contained as subsidiary elements to the fundamental electrodes. The filament 103 consists of very fine tungsten core wires coated with an oxide, e.g. barium, and radiates thermions when a voltage is applied thereto. The grid 104 is a metal mesh made of stainless steel or the like, and accelerates and distributes the thermions from the filament 103 to direct them to the anode 105 when a positive voltage is applied thereto. When a negative voltage is applied, the grid 104 blocks the thermions from the anode 105.
The anode 105 is constructed by printing a fluorescent object in a display pattern on a conductor that is made of carbon or the like and is formed to have a similar shape to the display pattern. When a positive voltage is applied to the anode 105, the thermions accelerated and distributed by the grid 104 are made clash with each other, and thus excite the fluorescent object to emit light. Designated by 108, 109, 110 and 111 are anode wiring, lead terminals, an exhausting pipe, and a getter. The exhausting pipe 110 is provided for letting internal air out of the vacuum container during the manufacture. The getter 111 absorbs residual air or gas to maintain the interior of the container vacuum.
Although the getter 111 absorbs the residual gas in the container of the fluorescent display panel 100, it has been found that the getter will release the absorbed gas again with time, so the effect is insufficient. For this reason, the fluorescent display panel 100 has a disadvantage that luminance of the fluorescent object will be lowered if the fluorescent display panel 100 is turned on after being left inactive for a long time, e.g. for more than 48 hours, because the residual air or gas that includes impurity is deposited on the fluorescent object during the inactive period. Therefore, where the fluorescent display panel is used as the printing head for the printer-incorporated electronic still camera, a problem arises from the above disadvantage that the average density of printed images would be lowered after the printing head is unused for a long time.